In the related art, there is known a method of creating a virtual endoscopic image based on 3-dimensional image data collected by a medical image diagnosis apparatus (hereinafter, referred to as a virtual endoscope (VE) method). Examples of the medical image diagnosis apparatus include an X-ray computed tomography (CT) apparatus, a magnetic resonance imaging (MRI) apparatus, an ultrasonograph apparatus, and the like. In the VE method, the image processing apparatus receives settings for a viewpoint position, a line-of-sight direction, and a field-of-view angle that centers on the line-of-sight direction. In addition, the image processing apparatus creates a projection image by perspectively projecting the 3-dimensional image data at a viewpoint position onto the range defined by a line-of-sight direction and a field-of-view angle.
Since the projection image created using the VE method is similar to an endoscope image obtained by observing a surface (internal surface) inside an organ using an endoscope, it is called a virtual endoscopic image (hereinafter, referred to as a fly-through image). For example, since a fly-through image created from the 3-dimensional image data obtained by capturing a vessel of a subject is similar to an endoscopic image obtained by observing a surface (a vascular wall) inside the vessel, it is used in an ischemic heart disease diagnosis. For example, JP-A 11-76228 (KOKAI) discloses a technique of synthesizing a cross-sectional image created from the 3-dimensional image data with a fly-through image.
However, the image processing apparatus of the related art only displays information on the surface of the projection image as described above, and fails to display, for example, information on spatial distribution such as a thickness of a plaque portion or a calcification portion formed in the vascular wall. For example, although the spatial distribution information on the plaque portion or the calcification portion is important in an ischemic heart disease diagnosis, the image processing apparatus of the related art cannot provide such information.